This invention concerns a device to heat the leading end of aluminum ingots to be extruded when hot in a turret-type extrusion press. The invention concerns also a method to heat the leading end of ingots to be extruded.
To be more exact, the invention concerns a device to heat the leading end part of aluminum ingots, the device being applied to the chamber for insertion and readying of the ingots.
According to the invention the heater device is located in cooperation with that part of the chamber which cooperates directly with the extruder die.
A press of this type is disclosed in EP-A-0318621.
It is known that during the hot extrusion operation the temperature of the ingot rises from about 400.degree. C. at the beginning to 500.degree. C. at the end.
This occurrence requires a greater initial thrust and a lesser final thrust since with an increase of the temperature it is necessary to reduce the extrusion pressure as a consequence.
Various arrangements have been studied in trying to keep the extrusion capacity constant, that is to say, in trying to keep the extrusion at a high and optimum value.
A first arrangement is to heat the ingot with conventional means to a greater extent in the part which will come in contact with the die at once and then to insert the ingot into the chamber just before the chamber is rotated to take up its extrusion position.
This is a good arrangement theoretically but in actual practice entails the drawback that the movement and positioning times are such as to nullify the benefits.
A second arrangement consists in cooling the trailing end of the ingot just before it is inserted in the chamber, but this arrangement too has not given good results and is also counterproductive from the point of view of energy.
Trials have also been conducted with heating the leading end of the ingot with a burner as that end is inserted into the chamber, but these trials have also given bad results owing to the short length thus heated of the ingot and owing to the embrittlement of the chamber due to the increase of temperature of its walls caused by the heating.
The present applicant has now found unexpectedly that it is possible to overcome the shortcomings of the state of the art and to achieve a plurality of advantages by means of the invention.